Have attempted a translation. Craziness. However, very impressed by @stephenfry 's German. : )

When setting up the basic position and the en- or decryption code as well as when en – or decrypting messages, the letter A (red lettering) must be visible in the first, left-hand window. The en- or decryption process must be repeated in its entirety should a different letter have been visible in the left window.